Pusher actuation in a printhead chip for an inkjet printhead

ABSTRACT

A plurality of nozzle arrangements ( 70 ) is positioned on the substrate ( 12 ) of printhead chip. Each arrangement includes a nozzle chamber structure ( 72, 74, 76, 78 ) positioned on the substrate and defines a nozzle chamber ( 80 ) from which ink is ejected. An ink-ejecting mechanism is operatively arranged with respect to the nozzle chamber structure. The ink-ejecting mechanism includes at least one moving component ( 106 ) displaceable to generate a pressure pulse within the nozzle chamber to eject ink. An actuator ( 92 ) is positioned on the substrate and has at least one working member ( 4 ) that is of a material having a coefficient of thermal expansion such that the working member is capable of substantially rectilinear expansion. An energy transmitting means interconnects the moving component and the working member so that energy generated by the working member as a result of expansion and subsequent contraction of the working member is transmitted to the moving component resulting in generation of said pressure pulse.

FIELD OF THE INVENTION

This invention relates to a printhead chip for an inkjet printhead. Moreparticularly, this invention relates to a printhead chip for an inkjetprinthead that incorporates pusher actuation in order to achieve inkdrop ejection.

BACKGROUND OF THE INVENTION

As set out in the above referenced applications/patents, the Applicanthas spent a substantial amount of time and effort in developingprintheads that incorporate micro electromechanical system (MEMS)-basedcomponents to achieve the ejection of ink necessary for printing.

As a result of the Applicant's research and development, the Applicanthas been able to develop printheads having one or more printhead chipsthat together incorporate up to 84 000 nozzle arrangements. TheApplicant has also developed suitable processor technology that iscapable of controlling operation of such printheads. In particular, theprocessor technology and the printheads are capable of cooperating togenerate resolutions of 1600 dpi and higher in some cases. Examples ofsuitable processor technology are provided in the above referencedpatent applications/patents.

Common to most of the printhead chips that the Applicant has developedis a component that moves with respect to a substrate to eject ink froma nozzle chamber. This component can be in the form of an ink-ejectingmember that is displaceable in a nozzle chamber to eject the ink fromthe nozzle chamber.

As is also clear from the above applications, Applicant has developed anumber of ways in which to achieve the ejection of ink from therespective nozzle chambers. A majority of these are based on theselection of a material having a coefficient of thermal expansion thatis such that, on a MEMS scale, expansion upon heating and subsequentcontraction upon cooling can be harnessed to perform work. The materialis formed to define at least part of a thermal actuator that includes aheating circuit. The heating circuit is shaped to be resistively heatedwhen a current passes through the circuit. The current is supplied tothe circuit in the form of pulses at a frequency that depends on theprinting requirements. The pulses are usually supplied from a CMOS layerpositioned on a substrate of the printhead chip. The pulses are shapedand have a magnitude that is also dependent on the printingrequirements. The generation and control of the pulses is by way of asuitable microprocessor of the type described in the above referencedapplications.

On a macroscopic scale, it is counter-intuitive to use the expansion andsubsequent contraction of material in order to achieve the performanceof work. Applicant submits that the perceived slow rate of expansion andcontraction would lead a person of ordinary skill in the field ofmacroscopic engineering to seek alternative energy sources.

On a MEMS scale, however, Applicant has found that expansion andcontraction of such a material can be harnessed to perform work. Thereason for this is that, on this scale, expansion and contraction arerelatively rapid and can transmit relatively high force.

There remains an issue of range of movement. While the expansion andcontraction are both rapid and forceful, Applicant has found that itwould be desirable for a mechanism to be provided whereby such rapidityand force of movement could be amplified at a region where the work isrequired to eject the ink.

A majority of the nozzle arrangements covered by the above applicationsand patents use differential expansion in the thermal actuator toachieve bending of the thermal actuator. This bending movement istransmitted to an ink-ejecting component that is either rectilinearly orangularly displaced to eject the ink.

Applicant has found that it would be desirable for simple rectilinearexpansion of a thermal actuator to be transmitted to an ink-ejectingcomponent, since such simple rectilinear expansion on a MEMS scale isrelatively efficient.

The Applicant has conceived this invention in order to achieve thedesired transmission and amplification of motion mentioned above.

SUMMARY OF THE INVENTION

According to the invention, there is provided a printhead chip for aninkjet printhead, the printhead chip comprising

-   -   a substrate; and    -   a plurality of nozzle arrangements that is positioned on the        substrate, each nozzle arrangement comprising        -   a nozzle chamber structure that is positioned on the            substrate and that defines a nozzle chamber from which ink            is to be ejected;        -   an ink-ejecting mechanism that is operatively arranged with            respect to the nozzle chamber structure, the ink-ejecting            mechanism including at least one moving component that is            displaceable to generate a pressure pulse within the nozzle            chamber to eject ink from the nozzle chamber;        -   an actuator that is positioned on the substrate and that has            at least one working member that is of a material having a            coefficient of thermal expansion such that the, or each,            working member is capable of substantially rectilinear            expansion and contraction when heated and subsequently            cooled; and        -   an energy transmitting means that interconnects the, or            each, moving component and the, or each, working member so            that energy generated by the, or each, working member as a            result of expansion and subsequent contraction of the, or            each, working member is transmitted to the, or each, moving            component resulting in displacement of the, or each, moving            component and generation of said pressure pulse.

The invention is now described, by way of examples, with reference tothe accompanying drawings. The following description is not intended tolimit the broad scope of the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a schematic view of a nozzle arrangement of a firstembodiment of a printhead chip, in accordance with the invention, for aninkjet printhead;

FIG. 2 shows a schematic view of a nozzle arrangement of a secondembodiment of a printhead chip, in accordance with the invention, for aninkjet printhead;

FIG. 3 shows a schematic view of a nozzle arrangement of a thirdembodiment of a printhead chip, in accordance with the invention;

FIG. 4 shows a schematic view of a nozzle arrangement of a fourthembodiment of a printhead chip, in accordance with the invention;

FIG. 5 shows a schematic view of a nozzle arrangement of a fifthembodiment of a printhead chip, in accordance with the invention;

FIG. 6 shows a schematic side view showing further detail of the nozzlearrangement of FIG. 5 in a quiescent condition;

FIG. 7 shows a schematic side view of the nozzle arrangement of FIG. 5in an operative condition;

FIG. 8 shows a schematic plan view of the nozzle arrangement of FIG. 5;and

FIG. 9 shows a schematic side view of a nozzle arrangement of a sixthembodiment of a printhead chip, in accordance with the invention, for aninkjet printhead.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, reference numeral 10 generally indicates a nozzle arrangementfor a first embodiment of an ink jet printhead chip, in accordance withthe invention.

The nozzle arrangement 10 is one of a plurality of such nozzlearrangements formed on a silicon wafer substrate 12 (FIG. 6) to definethe printhead chip of the invention. As set out in the background ofthis specification, a single printhead can contain up to 84 000 suchnozzle arrangements. For the purposes of clarity and ease ofdescription, only one nozzle arrangement is described. It is to beappreciated that a person of ordinary skill in the field can readilyobtain the printhead chip by simply replicating the nozzle arrangement10 on the wafer substrate 12.

The printhead chip is the product of an integrated circuit fabricationtechnique. In particular, each nozzle arrangement 10 is the product of aMEMS-based fabrication technique. As is known, such a fabricationtechnique involves the deposition of functional layers and sacrificiallayers of integrated circuit materials. The functional layers are etchedto define various moving components and the sacrificial layers areetched away to release the components. As is known, such fabricationtechniques generally involve the replication of a large number ofsimilar components on a single wafer that is subsequently diced toseparate the various components from each other. This reinforces thesubmission that a person of ordinary skill in the field can readilyobtain the printhead chip of this invention by replicating the nozzlearrangement 10.

An electrical drive circuitry layer 14 is positioned on the siliconwafer substrate 12. The electrical drive circuitry layer 14 includesCMOS drive circuitry. The particular configuration of the CMOS drivecircuitry is not important to this description and has therefore beenshown schematically in the drawings. Suffice to say that it is connectedto a suitable microprocessor and provides electrical current to thenozzle arrangement 10 upon receipt of an enabling signal from saidsuitable microprocessor. An example of a suitable microprocessor isdescribed in the above referenced patents/patent applications. Itfollows that this level of detail will not be set out in thisspecification.

An ink passivation layer 16 is positioned on the drive circuitry layer14. The ink passivation layer 16 can be of any suitable material, suchas silicon nitride.

The nozzle arrangement 10 is shown in FIG. 1 as broadly conceptual. Thenozzle arrangement 10 includes an actuator in the form of an electrothermal actuator 18. The actuator 18 includes an electrical resistiveheating circuit 20. The circuit 20 incorporates a working member in theform of a conductive heating element 22. The heating element 22 is of amaterial having a coefficient of thermal expansion that is such thatwhen the material is heated and subsequently cooled, the material iscapable of expansion and subsequent contraction to an extent sufficientto perform work on a MEMS-scale. Any of a number of materials used inintegrated circuit fabrication could be suitable. Such materials couldinclude gold, copper or titanium. The Applicant has found that titaniumaluminum nitride (TiAlN) is particularly suitable for this purpose.

Thermal expansion and contraction occurs per unit length of the heatingelement 22 as is known. The principle behind the nozzle arrangement 10is to provide the heating element 22 with sufficient length so that theextent of movement when the heating element 22 expands and contracts issufficient to generate useful energy. Thus, the length of the heatingelement 22 is a factor that defines a useful energy transmitting means.In particular, the heating element 22 is of a length which is such thatthe extent of movement is similar to the extent of movement of thecomponents of the nozzle arrangements described in the above referencedpatents/patent applications.

The heating element 22 is connected to an ink-ejecting mechanism in theform of an ink-ejecting member or piston 24. The piston 24 is positionedin a nozzle chamber structure 26. The nozzle chamber structure 26 hasnozzle chamber walls 28 and a roof 30. The roof 30 defines an inkejection port 32.

The heating element 22 has a fixed end 34 and a working end 36 so that,on expansion and contraction of the heating element 22, the working end36 is displaceable, in a rectilinear manner, with respect to the fixedend 34. This results in reciprocal movement of the piston 24 relative tothe roof 30 and subsequent ejection of ink from the ink ejection port32.

In FIG. 2, reference numeral 40 generally indicates a nozzle arrangementof a second embodiment of a printhead chip, in accordance with theinvention, for an inkjet printhead. With reference to FIG. 1, likereference numerals refer to like parts, unless otherwise specified.

Again the nozzle arrangement 40 is shown only conceptually. It isrespectfully submitted that a person of ordinary skill in the field ofMEMS fabrication could readily fabricate a nozzle arrangement thatutilizes the concept illustrated in FIG. 2.

The nozzle arrangement 40 also includes a heating circuit 42. However, aheating element 44 of the heating circuit 42 is a convenient length. Thenozzle arrangement 40 utilizes a hydraulic principle in order to achievea useful force transmitting means. In this embodiment, a cross sectionalarea of the piston 24 and thus the nozzle chamber 26 are a sufficientlyhigh number of orders of magnitude larger than a cross sectional area ofthe ink ejection port 32. Thus, a required extent of movement of thepiston 24 can be reduced considerably from what would usually berequired in the nozzle arrangements described in the above referencedapplications, while still achieving drop ejection.

In FIG. 3, reference numeral 50 generally indicates a nozzle arrangementof a third embodiment of a printhead chip, in accordance with theinvention, for an inkjet printhead. With reference to FIGS. 1 and 2,like reference numerals refer to like parts, unless otherwise specified.

The nozzle arrangement 50 is again shown as broadly conceptual. Inparticular, the nozzle arrangement 50 illustrates that instead of havingthe dimensional configurations described in the previous embodiment, asuitable motion amplifying means 52 can be positioned between theheating element 44 and the piston 24. The motion amplifying means 52 cantake a number of different forms. In particular, the motion amplifyingmeans can be in the form of a conventional micro mechanical arrangementsuch as a gearing system.

In FIG. 4, reference numeral 60 generally indicates a nozzle arrangementof a fourth embodiment of a printhead chip, in accordance with theinvention, for an inkjet printhead. With reference to FIGS. 1 to 3, likereference numerals refer to like parts, unless otherwise specified.

The nozzle arrangement 60 is shown as broadly conceptual. In thisembodiment, a lever mechanism 62 is positioned intermediate the workingend 36 of the heating element 44 and the piston 24. The lever mechanism62 has an effective effort arm 64 connected to an effective load arm 66with a fulcrum 68. It is to be noted that the lever mechanism 62 shownin FIG. 4 is schematic and that any of a number of micro mechanicalsystems defining lever mechanisms 62 can be used.

The lever mechanism 62 is configured so that the effective load arm 66is between approximately 20 and 60 times longer than the effectiveeffort arm 64. In particular, the lever mechanism 62 is configured sothat the effective load arm 66 is approximately 40 times longer than theeffective effort arm 64.

In FIGS. 5 to 8, reference numeral 70 generally indicates a nozzlearrangement of a fifth embodiment of a printhead chip, in accordancewith the invention, for an inkjet printhead. With reference to FIGS. 1to 4, like reference numerals refer to like parts, unless otherwisespecified.

The nozzle arrangement 70 includes nozzle chamber walls in the form of adistal end wall 72, a proximal end wall 74 and a pair of opposedsidewalls 76. A roof 78 spans the walls 72, 74, 76. The roof 78 and thewalls 72, 74, 76 define a nozzle chamber 80. The roof 78 defines an inkejection port 82 in fluid communication with the nozzle chamber 80. Thewalls 72, 74, 76 and the roof 78 are dimensioned so that the nozzlechamber 80 has a rectangular shape when viewed in plan. The ink ejectionport 82 is positioned adjacent a distal end 84 of the nozzle chamber 80.

A plurality of ink inlet channels 86 is defined through the substrate 12and the layers 14, 16. Each ink inlet channel 86 is in fluidcommunication with a respective nozzle chamber 80. Further, an opening88 of each ink inlet channel 86 is aligned with the ink ejection port 82of its associated nozzle chamber 80.

An anchor formation in the form of a pair of anchors 90 is fast with thesubstrate 12 on a proximal side of the nozzle chamber 80. The heatingcircuit 44 includes an electro thermal expansion actuator 92 that isfast with the anchors 90 and extends towards the proximal end wall 74.The thermal expansion actuator 92 is of a conductive material and isshaped to define part of the heating circuit 44. The actuator 92 is of amaterial that has a coefficient of thermal expansion that is such that,when heated and subsequently cooled, expansion and contraction of thematerial can be harnessed to perform work on a MEMS scale. An example ofa suitable material is TiAlN. In particular, the thermal expansionactuator 92 has a pair of arms 94 that are interconnected by a bridgeportion 96. The actuator 92 has a fixed portion defined by fixed ends 98of the arms 94 that are fast with respective anchors 90.

Each of the anchors 90 are configured to provide electrical connectionbetween the fixed ends 98 and the electrical drive circuitry layer 14.In particular, the anchors 90 are configured to provide electricalconnection between one fixed end 98 and a negative contact and the otherfixed end 98 and a positive contact. The electrical drive circuitrylayer 14 is connected to a microprocessor of the type described in theabove referenced patents/applications so that electrical current pulsesof suitable shape and magnitude can be supplied to the actuator 92.

The bridge portion 96 of the actuator 92 defines a working portion ofthe actuator 92.

The nozzle arrangement 70 includes a pivot member 100 that is pivotallyarranged on the proximal end wall 74. The bridge portion 96 of theactuator 92 is connected to the pivot member 100 at a positionintermediate a pivot point, indicated at 102, defined by the pivotmember 100 and the proximal end wall 74. It is to be understood that thepivot point 102 can be defined by any number of configurations of thepivot member 100 and the proximal end wall 74. For this reason, thepivot point 102 is indicated schematically only. In one possibleembodiment, the proximal end wall 74 could define the pivot member 100.In this case, the pivot point 102 would be defined between the proximalend wall 74 and the sidewalls 76. In particular, this would entailhingedly connecting the proximal end wall 74 to the sidewalls 76.

It will be appreciated that, in any event, the pivot member 100 is toform part of the proximal end wall 74. Thus, a sealing member 104 isprovided intermediate the pivot member 100 and the ink passivation layer16. The sealing member 104 is configured to accommodate pivotal movementof the pivot member 100 upon expansion and subsequent contraction of thethermal expansion actuator 92.

The nozzle arrangement 70 includes an ink ejection member in the form ofa paddle 106. The paddle 106 is dimensioned to correspond generally withthe nozzle chamber 80. In particular, the paddle 106 is dimensioned sothat an end portion 108 of the paddle 106 is positioned intermediate theink ejection port 82 and the opening 88 of the ink inlet channel 86.

The paddle 106 and the pivot member 100 are configured so that thepaddle 106 is between approximately 20 and 60 times longer than aneffective lever arm, indicated at 110, defined by the paddle 106 and thepivot member 100. In particular, the paddle 106 can be approximately 40times longer than the effective lever arm 110. It should be noted thatthe lever arm 110 is only shown schematically because of the widevariety of different possible configurations available for defining thelever arm 110. Further, a ratio of paddle length to lever arm length canvary widely from the 40:1 ratio. This could depend on a number offactors such as driving signal strength and actuator material. Forexample, in one embodiment, the Applicant has devised the actuator 92 toexpand by 50 nanometers while the end portion 108 of the paddle 106moves through between 1 and 2 microns.

It will be appreciated that a maximum extent of movement of the paddle106 takes place at the end portion 108 of the paddle 106. Furthermore,this extent of movement is up to 40 times greater than a range ofmovement of the effective lever arm 110. It follows that the expansionof the thermal actuator 92 is substantially amplified at the end portion108, therefore facilitating the ejection of ink 112 from the inkejection port 82 as indicated at 114 in FIG. 7. When the actuator 92cools, subsequent contraction of the actuator 92 causes an amplifiedextent of movement of the end portion 108 back into a quiescent positionshown in FIG. 6. This results in separation of the ink 114 from the ink112 to form an ink drop 116.

The paddle 106 includes reinforcing ribs 118 to strengthen the paddle106. This is necessary due to the relative length of the paddle 106 anda resultant bending moment exerted on the paddle 106.

It will be appreciated that, in light of the above referencedapplications and patents, the nozzle arrangement 70 is suited forfabrication with an integrated circuit fabrication technique.Furthermore, the pivot member 100 and pivot point 102 can be defined byany number of micro mechanical arrangements. For example, a flexiblemember may be formed intermediate the pivot member 100 and the sidewalls76 or proximal end wall 74 that is distorted to accommodate pivotalmovement of the pivot member 100.

In FIG. 9, reference numeral 120 generally indicates a nozzlearrangement of a sixth embodiment of a printhead chip, in accordancewith the invention, for an inkjet printhead. With reference to FIGS. 1to 8, like reference numerals refer to like parts, unless otherwisespecified.

The nozzle arrangement 120 includes a nozzle chamber structure in theform of an active ink-ejecting structure 122. The active ink-ejectingstructure 122 has a roof 124 and walls 126 that extend from the roof 124towards the substrate 12. The roof 124 defines an ink ejection port 128.The roof 124 and the walls 126 together define a nozzle chamber 130.

The walls 126 comprise a proximal end wall 132, an opposed distal endwall 134 and a pair of opposed sidewalls 136. The ink ejection port 128is positioned adjacent the distal end wall 134, while the opening 88 ofthe ink inlet channel 86 is positioned adjacent the proximal end wall132.

The proximal end wall 132 is pivotally mounted on the substrate 12 sothat the active ink-ejecting structure 122 is pivotal with respect tothe substrate 12. In particular, the active ink-ejecting structure 122is pivotal in the direction of an arrow 138 to an extent that issufficient to facilitate the ejection of ink from the ink ejection port128.

The roof 124 and the walls 126 are dimensioned so that the nozzlechamber 130 is rectangular and has a length that is more than 3 times aheight of the nozzle chamber 130. This, together with the fact that theink ejection port 128 and the opening 88 are positioned at opposite endsof the nozzle chamber 130 facilitates the retardation of ink flow fromthe ink ejection port 128 towards the opening 88 when the structure 122is pivotally displaced towards the substrate 12. This flow is referredto as backflow and is highly undesirable.

The bridge portion 96 of the actuator 92 is fixed to the proximal endwall 132. Thus, on heating and subsequent expansion of the actuator 92in the manner described above, the ink-ejecting structure 122 is pivotedtowards the substrate 12. Upon cooling and subsequent contraction of theactuator 92 in the manner described above, the ink-ejecting structure122 is pivoted away from the substrate 12. This reciprocal movement ofthe ink-ejecting structure 122 results in the ejection of an ink dropfrom the ink ejection port 128.

The bridge portion 96 is connected to the proximal end wall 132 at aposition in which a length of the ink-ejecting structure 122 is up to 40times greater than a length of an effective lever arm, indicated at 140.It follows that pivotal movement of the effective lever arm 140 as aresult of displacement of the bridge portion 96 upon heating andsubsequent cooling of the actuator 92 can be amplified by a factor ashigh as 40. It has been found by the Applicant that this facilitatesefficient ink drop ejection.

The nozzle arrangement 120 includes a sealing structure 142 that extendsfrom the ink passivation layer 16. The walls 126 overlap the sealingstructure 142 so that a fluidic seal is defined between the sealingstructure 142 and the walls 126 when the nozzle chamber 130 is filledwith ink.

Applicant believes that this invention provides a means whereby simplethermal expansion and contraction, in a rectilinear manner, can beconverted into useful work.

1. A printhead chip for an inkjet printhead, the printhead chipcomprising a substrate; and a plurality of nozzle arrangements that ispositioned on the substrate, each nozzle arrangement comprising a nozzlechamber structure that is positioned on the substrate and that defines anozzle chamber from which ink is to be ejected; an ink-ejectingmechanism that is operatively arranged with respect to the nozzlechamber structure, the ink-ejecting mechanism including at least onemoving component that is displaceable to generate a pressure pulsewithin the nozzle chamber to eject ink from the nozzle chamber; anactuator that is positioned on the substrate and that has at least oneworking member that is of a material having a coefficient of thermalexpansion such that the, or each, working member is capable ofsubstantially rectilinear expansion and contraction when heated andsubsequently cooled; and an energy transmitting means that interconnectsthe, or each, moving component and the, or each, working member so thatenergy generated by the, or each, working member as a result ofexpansion and subsequent contraction of the, or each, working member istransmitted to the, or each, moving component resulting in displacementof the, or each, moving component and generation of said pressure pulse.2. A printhead chip as claimed in claim 1, which is the product of anintegrated circuit fabrication technique.
 3. A printhead chip as claimedin claim 2, in which the substrate includes a silicon wafer substrateand a CMOS drive circuitry layer positioned on the silicon wafersubstrate.
 4. A printhead chip as claimed in claim 3, in which eachactuator includes one elongate working arm that has a fixed end portionand a working end portion, the working arm being configured to definepart of a resistive heating circuit, the working arm also beingelectrically connected to the drive circuitry layer so that a currentpulse can be set up in the working arm to displace the working endportion relative to the fixed end portion upon heating and subsequentcooling of the working arm as a result of the current pulse.
 5. Aprinthead chip as claimed in claim 4, in which each nozzle chamberstructure includes nozzle chamber walls and a roof positioned on thenozzle chamber walls, the roof defining an ink ejection port from whichink is ejected upon generation of said pressure pulse.
 6. A printheadchip as claimed in claim 5, in which each ink-ejecting mechanismincludes one moving component in the form of an ink-ejecting member thatis positioned in the nozzle chamber and is displaceable towards and awayfrom the roof to generate said pressure pulse.
 7. A printhead chip asclaimed in claim 6, in which the energy transmitting means is defined bythe ink-ejecting member having an ink-ejecting surface area that is apredetermined order of magnitude larger than an opening area of the inkejection port so that a hydraulic advantage is achieved.
 8. A printheadchip as claimed in claim 6, in which the energy transmitting means is inthe form of a motion amplification means that is configured so thatmovement of the ink-ejecting member is a predetermined order ofmagnitude greater than that of the working end portion of the workingmember.
 9. A printhead chip as claimed in claim 8, in which the motionamplification means includes a lever mechanism, the lever mechanismdefining an effort arm that is connected to the working end portion ofthe working member and the ink-ejecting member defining a load arm, theload arm having an effective length that is a predetermined order ofmagnitude greater than an effective length of the effort arm, the levermechanism further defining a fulcrum that connects the effort and loadarms pivotally to one of the substrate and the nozzle chamber structure.10. An inkjet printhead that includes at least one printhead chip asclaimed in claim 1.